Veneer inspection system

ABSTRACT

On-line apparatus for inspecting a moving strip of veneer for the presence of cracks, knotholes, voids and similar type wood defects utilizing light transmission through the material to detect discontinuities therein. Light radiation transmitted through such a wood defect is detected by a scanner head formed of a plurality of flexible, light-conducting optical fibers whose terminal ends are positioned adjacent the surface of the veneer strip on the side opposite the light source and at spaced locations along the transverse width of the strip. The detected light radiation is conveyed by the flexible fibers to a corresponding array of photoelectric transducers which are strobe interrogated in serial sequence so as to generate as an output a composite waveform indicative of the light transmissibility pattern of the cross-section of veneer strip passing over the scanner head at the instant of the strobe. This strobe interrogation process is repeated at regular close intervals, so as to generate successive waveforms representative of the character of the wood strip passing over the scanner head. The presence of through-wood defects produces corresponding variations in the successive waveform outputs of the photosensor array which, after digitizing, are fed into arithmetic and logic circuitry. Counter and comparator elements operate on this digital information to measure the cross-grain and with-grain dimensions of individual defects and generate an actuating signal when a defect exceeds predetermined dimensional limits. The logic circuitry distinguishes cracks and splits on the one hand, which have large with-grain and quite narrow cross-grain dimension, from knotholes and other voids in the wood having substantially larger cross-grain dimension than cracks or splits.

Unite States Patent Watson et a1.

[54] VENEER INSPECTION SYSTEM [72] Inventors: Gerald L. Watson, Tigard;Don

Latshaw, Portland, both of Greg.

[73] Assignee: Morvue, lnc., Tigard, Oreg.

[22] Filed: Oct. 22, 1970 [21] Appl. No.: 83,075

[52] US. Cl ..250/219 DF, 250/219 WE, 250/227,

356/199, 356/237 51 Int. Cl. ..G01n 21/30 58 Field ofSearch ..250/2195219 R, 219 D,

2 19 FR, 250/219 WE,2I9 DF,227 350/96; 356/199, 200, 237, 238

Primary Examiner-James W. Lawrence Assistant ExaminerD. C. NelmsAttorney-Daniel P. Chemoff [451 Sept. 26, 1972 57 ABSTRACT On-lineapparatus for inspecting a moving strip of veneer for the presence ofcracks, knotholes, voids and similar type wood defects utilizing lighttransmission through the material to detect discontinuities therein.Light radiation transmitted through such a wood defect is detected by ascanner head formed of a plurality of flexible, light-conducting opticalfibers whose terminal ends are positioned adjacent the surface of theveneer strip on the side opposite the light source and at spacedlocations along the transverse width of the strip. The detected lightradiation is conveyed by the flexible fibers to a corresponding array ofphotoelectric transducers which are strobe interrogated in serialsequence so as to generate as an output a composite waveform indicativeof the light transmissibility pattern of the cross-section of veneerstrip passing over the scanner head at the instant of the strobe. Thisstrobe interrogation process is repeated at regular close intervals, soas to generate successive waveforms representative of the character ofthe wood strip passing over the scanner head. The presence ofthrough-wood defects produces corresponding variations in the successivewaveform outputs of the photosensor array which, after digitizing, arefed into arithmetic and logic circuitry. Counter and comparator elementsoperate on this digital information to measure the cross-grain andwith-grain dimensions of individual defects and generate an actuatingsignal when a defect exceeds predetermined dimensional limits. The logiccircuitry distinguishes cracks and splits on the one hand, which havelarge withrain and quite narrow cross-grain dimension, rom

knotholes and other voids in the wood having substantially largercross-grain dimension than cracks or splits.

3 Claims, 11 Drawing Figures PATENTEIJSEP26 I972 SHEET 2 0F 5 mm lP'A'TENTEnsivzs I972 sum 3 or 5 380 {38b {38c {38d (38e PHOTO- PHOTO-PHOTO- PHOTO- PHOTO- SENSOR SENSOR SENSOR SENSOR SENSOR o b c d e y f\f\ fL y f\ f\ ANALOG ANALOG swn'c SWITCH SCANNER F I G, 4 OUTPUT STROBEPROCESS PHOTOSENSOR OUTPUT I d k 55 V fl* Z A SCANNER OUTPUT VOLTAGETHRESHOLD DETECTOR OUTPUT Fl G. 5

P'ATEmEflsms 1972 SHEET 0F 5 DETECTOR SCAN LINE I5 FIG. 6b

SUCCESSIVE THRESHOLD OUTPUTS H6. 66 CONTENTS OF ACCUMULATOR VENEERINSPECTION SYSTEM BACKGROUND OF THE INVENTION This invention relates toapparatus for on-line inspection of moving veneer strip for through-wooddefects, and more particularly relates to veneer inspection apparatuswith means for measuring the size of such defects and generating anactuating signal output when the dimensions of a defect exceedpredetermined limits.

In the production of wood veneer, wherein a ribbon of wood of typicallyone-tenth to two-tenths of an inch thickness is peeled from a log by aveneer lathe, there inevitably appear on the veneer strip at regular andirregular intervals various dicontinuities or throughwood defects in theform of cracks, splits, knotholes, fishtails, voids and the like.Depending upon the size of such defects, both in their with-grain andcross-grain dimensions, it is desirable, in accordance with industrypractice, to clip them out from the traveling strip with a veneer knifewhen the defect exceeds certain tolerance limits.

Until fairly recently the operation of the veneer knife was under themanual control of a human operator (the clipperrnan) who visuallymonitored the quality and character of the veneer strip and actuated theguillotine-like knife to cut out the unacceptable portions of veneercontaining oversized wood defects. Because of the speed of the striptravel, as well as the frequency of the clipping action required of theoperator, considerable wood wastage occurred as it was impossible forthe operator to cut the wood at precisely the leading and trailing edgesof the defect, thus leaving sizeable marginal bands of good wood oneither side which would be clipped out with the defect. Also, theoperator was subject to fatigue and human error, thereby increasing thepossibility that sizable amounts of good wood would be wasted in theclipping process. Moreover, the decision of the clipperrnan, as towhether to clip out or leave in a small defect not clearly exceeding theprescribed tolerance limits was a subjective one and accordinglysusceptible to variation from time to time with the same operator andfrom shift to shift with different operators. Finally, it was essentialfor best clipping results that the travel of the veneer strip be at arelatively slow speed within the ability of the clipper operator tovisually scan the veneer for defects as it passed beneath his gaze.Consequently, veneer clipping, when carried out by human operators, isan inefficient, tedious; wasteful and costly process.

Apparatus has recently been devised by applicants assignee, marketedunder the trademark Autoclip and disclosed in its Watson et al US. Pat.No. 3,560,096, in which veneer strip is inspected for wood defects byelectro-optical means and the clipper knife actuated automatically whena defect exceeds certain predetermined dimensional limits. In this priorapparatus de fects are detected by monitoring the variations in lightintensity reflected from the surface of the wood as it passes beneath anillumination source. While this device performs satisfactorily, it is ofsomewhat intricate and expensive construction since it is necessary toemploy a relatively complex optical arrangement and computer circuitryin order to enable the system to compensate for stain and similarvariations in reflected light intensity caused by surface discolorationsin the beneath the traveling veneer strip on the side opposite veneerfrom through-wood defects such as knotholes, cracks, voids and the likewhich deleteriously affect its structural integrity and strength.

In order to simplify the design and lower the cost of an automaticinspection system capable of reliably detecting and monitoring the sizeof through-wood type defects in veneer strip as it travels by at a highrate of speed so as to generate an actuating signal for the clipperknife when a defect exceeds predetermined dimensional limits, thepresent applicants have devised a novel apparatus utilizing a scannerhead positioned an illumination source and responsive to light radiationpassing through the wood at those places where throughwood type defectsare present. In this manner the complexities introduced in theaforementioned prior art device occasioned by surface discolorations andirregularities not materially affecting the structural integrity of thematerial are inherently eliminated, thus greatly reducing the cost ofthe veneer inspection system, with the only sacrifice in system responsebeing with respect to detecting superficial wood irregularities andsurface discolorations which are of usually lesser importance.

SUMMARY OF THE INVENTION The present invention is directed to a veneerinspection system in the form of apparatus for detecting and monitoringthe size of through-the-wood defects in a moving strip of veneer and forgenerating an actuating signal for controlling a clipper knife when adefect exceeds predetermined limits either on its with-grain size or ona combination of its with-grain and cross-grain size. The apparatusutilizes an illumination source on one side of the wood strip and ascanner situated on the other side responsive to light energytransmitted through any openings appearing in the material passingbetween. The scanner is comprised of a head element formed of a glassrod, extending laterally of the veneer strip and contacting theunderside of the wood, to which are connected at closely spacedintervals along the length of therod the terminal ends of a plurality oflight-conducting optical fibers. The array of optical fibers receivesany light energy transmitted through any respectively opposed openingsappearing in the veneer strip as it passes over the rod and transmitsthe light to a corresponding array of photo-electric transducers whichconvert the incident light energy to an electrical output.

The electrical signals derived from the respective outputs of theindividual photosensors are representative of the pattern of lightenergy transmitted through openings appearing in the wood material as itpasses over the scanner head. These photosensor signals are thenconverted into a serial pulse train waveform by periodic strobeinterrogation of the sensors in sequence under control of a timing clockpulse followed by digitizing of the information so obtained through theuse of a threshold detector limiter. Thus, at regular intervals ofincremental advance of the veneer strip past the scanner head, a pulsetrain ,is generated which is representative of the instantaneous lighttransmisson pattern across the width of the veneer at the plane of thescanner head. (Generally speaking, the pulse train representative of thelight transmissibility pattern is in binary bit form since, at eachdetection point in the scanner head along the width of the veneer, thelight from the illumination source at any given instant of time iseither blocked by the wood or is substantially or wholly transmittedtherethrough due to the presence of a void or discontinuity in the woodat that point.) The pulse train waveforms generated by the photosensorsare supplied to suitable arithmetic and logic circuitry which count thenumber of pulses in a given train (indicative of the with-grain size ofa defect) and compare successive pulse trains (indicative of thecross-grain size of a defect), and then in turn compare these readingswith preset dimensional limits to generate output signals whentolerances are exceeded. In the foregoing manner the traveling veneerstrip is constantly monitored by the apparatus for the presence ofthrough-wood defects, their size noted and an actuating signal generatedwhen the size of any such defect exceeds acceptable limits.

It is therefore a principal objective of the present invention toprovide a novel apparatus for on-line inspection of a moving strip ofveneer whose response to the presence of through-wood defects is notaffected by surface discolorations and irregularities occurring in theveneer and which is of more simplified and economical design than priorart devices heretofore utilized for this purpose.

It is a further objective of the present invention to provide, in aveneer inspection apparatus of the type described, computer means forgenerating an actuating signal output when the apparatus detects thepresence of a throughwood defect in the traveling veneer strip whosewith-grain size, or the combination of with-grain and cross-grain size,exceeds predetermined dimensional limits.

It is a principal feature of the present invention to provide anapparatus for on-line inspection of a moving strip of veneer whichutilizes light transmission through the material to detect the presenceand monitor the size of through-wood defects appearing therein.

It is a further principal feature of the present invention to provide anovel and improved form of scanner, for use in detecting the presence ofdiscontinuities in a moving strip of material, which is comprised of ascanner head formed of a plurality of light-conducting optical fiberswhose terminal ends are positioned adjacent the surface of the materialon a side opposite an illumination source and at spaced locations alongthe transverse width of the material, in conjunction with acorresponding array of photoelectric transducers which are strobeinterrogated in serial sequence so as to generate as an electricaloutput a composite waveform indicative of the light transmissibilitypattern of the cross-section of material passing over the scanner headat the instance of the strobe.

The foregoing and other objectives, features and advantages of thepresent invention will be more readily understood upon consideration ofthe following detailed description of the invention, taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial perspective viewof an illustrative embodiment of the veneer inspection apparatus of thepresent invention.

FIG. 2 is an exploded pictorial view of an exemplary form of scannerhead employed in the veneer inspection apparatus of the presentinvention.

FIG. 3 is an exploded pictorial view of the electrooptical interfaceassembly connecting the optical fibers of the scanner head to acorresponding array of photosensor elements in a veneer inspectionapparatus of the present invention.

FIG. 3A is a sectional view of a portion of the electro-opticalinterface in assembled form, taken along the plane 3A-3A in FIG. 3.

FIG. 3B is a sectional view of the electrooptical interface taken alongthe plane 38-38 in FIG. 3A.

FIG. 4 is a schematic diagram of an exemplary circuit means for strobeinterrogation of the array of photosensor elements for generation of apulse wavetrain representative of the instantaneous lighttransmissibility pattern of the veneer material under inspection by theapparatus.

FIG. 5 is a waveform diagram illustrating the output of a typicalphotosensor element when a through-wood opening in veneer material issensed by it corresponding optical fiber element in the scanning head,together with a waveform diagram showing the resultant electrical signaloutput after it has been digitized by a threshold limiter.

FIGS. 6a 6c are a series of diagrams illustrating the operation of thecomputer portion of the apparatus on a typical series of pulse trainsgenerated by the scanner as a through-wood defect travels past thescanner head.

FIG. 7 is a block diagram of the arithmetic and logic elementscomprising the computer portion of the veneer inspection apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,FIG. 1 depicts an illustrative embodiment of an on-line apparatus forinspecting veneer ribbon in accordance with the teachings of the presentinvention. A veneer strip 10, as peeled from the log by the veneerknife, typically contains numerous through-wood defects such asknotholes l2, splits on cracks l3, fishtail or wane l4 and the like. Theveneer ribbon is carried by a conveyor belt arrangement 15 past theinspection apparatus which comprises an illumination source 18projecting light of relatively high intensity onto a scanner head 20extending transversely across the width of the veneer and in proximaterelation to the bottom surface thereof as it passes underneath the lightsource. The illumination source 18 may exemplarily be comprised of apair of high-lumen tungsten linear-filament lamps l9 projecting aguideline light beam of high intensity onto the veneer strip as itpasses underneath so that any defect extending wholly or substantiallythrough the thickness of the material will permit a substantial amountof light radiation to pass through at that point onto the underlyingscanner head 20.

The scanner head, the details of which are depicted in FIG. 2, comprisesa longitudinally-extending cylindrical rod 22 of glass orwear-resistanthard plastic extending transversely across the direction of travel ofthe veneer strip and bracketed on either side by a' pair of plates 24which support the roller mechanisms for the conveyor belt 15 and alsoserve as guide surfaces for the veneer as it passes over the scannerhead. The glass rod 22, which is sufficiently transparent to permitlight radiation to pass diametrically therethrough without substantialattenuation, is secured on a base member 26 so as to be in contact withthe undersurface of the veneer strip as it passes over the scanner head.The moving wood wipes the surface of the rod 22 so as to maintain itclean of dust, pitch and other foreign matter.

Spaced at regular close intervals along the length of the rod 22, and incontact therewith at points diametrically beneath the portion of the rodsurface over which veneer material passes, is a plurality of flexible,lightconducting optical fibers 27 whose respective terminal ends aresecured inside the base member by a suitable fastener assembly 28. In anexemplary arrangement the array of glass fibers mig'ht typically bespaced on oneinch centers along the width of the veneer strip so that,for monitoring veneer of nominally eight-foot width, some hundred or soindividual optical fibers 27 would be contained in the array.

Any light radiation falling on the scanner head as a result of thepresence of through-wood defects in the veneer strip passing thereoveris conducted by the optical fibers to an electro-optical interfaceassembly 30, the details of which are depicted in FIGS. 3, 3A and 33,contained, along with the remainder of the components of the system,inside a cabinet housing 29 positioned off to one side of the conveyorfor easy access by personnal and energized from a suitable source ofelectrical potential. The electro-optical interface assembly comprises ablock member 32 securing the respective ends of the array of opticalfibers 27 and mating inside a keyway channel 34a formed inside a holdermember In forming the assembly, the array of optical fibers 27 is passedthrough holes 35 drilled in the block member 32 and secured insideeither by a friction fit or by an adhesive so as to terminatesubstantially flush with the upper surface 32a of the block. Positionedopposite the end of each of the optical fibers 27 is a respectivephotosensor (or photo-electric transducer element) 38 which ispositioned inside a corresponding hole 39 formed in the holder member34. The photosensor element, which may be of any suitable type known tothe art, converts light radiation incident thereon into a correspondingelectrical output whose amplitude is a function of the incident lightradiation.

interposed between the input or light-receiving end of each of thephotosensors and the terminal end of its associated optical fiberconveying light from the scanner head is a shutter element 40 in theform of a thin, short strip of opaque material. The shutter, which maybe positioned so as to block off a portion of the light which wouldotherwise be transmitted by the optical fiber to the photosensor,permits the respective outputs of the array of optical fibers andassociated photosensors to be normalized so that each produces anelectrical output of approximately the same amplitude under equivalentconditions of illumination at the scanner head. The positioning of theshutter strip 40 within the holder member 34, so as to block off therequisite portion of the light transmission from the fiber end to thephotosensor, may be readily accomplished with a pointed tool engaging amating indentation 40a formed on the upper surface of the strip.

The electrical leads carrying the respective outputs of the photosensors38 are connected to associated electrical components 42 carried on aprinted circuit board 45 secured by fasteners 46 to the holder member toform a compact and ruggedized assembly. The array of electrical outputsderived in the electro-optical innerface assembly which arerepresentative of the light energy incident on the scanner head isconnected by a connector'terminal 45a to the remaining electronicsportion of the system containing the digitizing logic and arithmeticsections.

Proceeding to the electronics portion of the system and referringinitially to FIG. 4, the respective outputs of the array of photosensors38a. .38e is subjected to a sequential interrogation by a strobe processto effect a parallel to serial conversion of the photodector outputs.Under control of a timing clock and switching circuit (not shown butconventional), a series of enabling pulses are applied in sequence overlines 1,. .y so as to momentarily turn on the respective analog switches50a. 50e connected to the individual photosensor outputs so that theresultant scanner output appearing on lead 52 is a composite waveformrepresenting the light transmissibility'pattern across the width of theveneer strip at the instant in time when the strobe interrogation iseffected. After a suitable period of time, corresponding to anincremental travel of the veneer strip past the scanner head (e.g.,one-tenth of an inch or so), the strobe interrogation process isrepeated and a new light transmissibility pattern, corresponding to thenew crosssection of material examined, is generated. The initiation ofeach strobe interrogation may be determined, as shown in FIG. I forexample, by counter wheel in contact with the surface of the movingstrip of veneer 10 closing a contact 101 following each revolution ofthe wheel, or a designated portion thereof, so as to generate a signal102 which can then be shaped into a suitable clock pulse.

The voltage vs. time waveform diagrams of FIG. 5 illustrate,respectively, a portion of the scanner output within a single strobesequence and the same output after the digitizing thereof by a thresholddetector. In the upper diagram the respective outputs of thephotosensors 38a. 38e are shown as forming the composite scanner output52 taken over the period of a single strobe interrogation. For theexemplary waveform shown it is assumed that, with respect to all but oneof the photodetectors in the group, no significant light radiation issensed at the respective fiber locations in the scanning head. Withrespect to photosensor 38d there is substantial light transmission dueto some type of through-wood defect occurring in the wood passing overthe end of its corresponding optical fiber 27 at the instant of thestrobe interrogation. As to the other photomonitoring points, someslight light transmission is noted, such as by photosensor 38b, due tothe semi-translucent character of the thin veneer material in thepresence of minute irregularities not extending substantially throughthe wood crosssection, but no other defect similar to that indicated byphotosensor 38d as extending substantially through the material ispresent at this particular instant in time.

In order to discriminate between through-wood defects which permitsubstantial amounts of light energy to pass through, and the minuteirregularities which sometimes produce a slight amount of lighttransmission, a threshold level 55 is established by means of athreshold detector/limiter circuit of any suitable known design so thatvoltage levels below the threshold are quantified by limiting action tothe same level, regardless of their input magnitude. In this manner,through the action of the threshold detector circuit, the scanner outputis digitized so as to produce a serial pulse train, consisting of 1s andOs, representing in each strobe interrogation sequence, the presence orabsence respectively at scanner detection points a. .n of through-wooddefects along the cross-section of veneer material passing over thescanner at the instant of the strobe.

Referring now to FIGS. 6a-6c, the series of diagrams illustrate theoperation of the input to the computer in the veneer inspection systemof the present invention. In FIG. 6a the veneer strip 10, traveling inthe direction indicated by the arrowhead ll (i.e., from bottom to top ofthe figure), passes across the plane'of the scanner 15. A typicalthrough-wood defect in the form of a split or a crack 13 extendstransversely across the width of veneer somewhat skewed butsubstantially parallel with the grain direction. At increments of timet, t representing successive initiations of the strobe interrogationsequence under control of the timing clock and corresponding toincremental advances of the strip over the scanner head, the respectivescanner detection points a. .e, being only a portion of the total in thescanner head array and corresponding to an adjacentset of spacedterminalends of the optical fibers 27, scan the wood at the instant of thestrobe for the transmission of light radiation through the material fromthe illumination source.

FIG. 6b shows a series of waveform diagrams taken at the same successiveintervals of time t,. .t which represent corresponding composite(strobe-interrogated) outputs of the respective photodetector elementsassociated with the scanner points a. e respectively after digitizing bythe threshold detector circuit. Thus, at instant of time t,, onlyscanner point a of the array will be positioned under the void formed inthe veneer strip by the crack defect l3 and thus the output of thethreshold detector will produce a single pulse at position a in thetrain shown in the uppermost diagram for the time instant At the timeinstant t both scanner points a and b will be in the void area andconsequently pulses will be produced at the corresponding time locationsa and b in the pulse train as indicated in the second diagram. Incorresponding fashion pulse train outputs at time instants t;,, t t etc.will reflect the presence or absence of voids in the strip material atthe respective scanner detection points at the instant of the strobeinterrogation.

The pulse train outputs of the threshold detector, representing in theform of successive waveforms the composite-light transmission pattern ofcorresponding cross-sections of the veneer strip as it passes over thescanner head 15, is supplied as an input to the logic portion of thecomputer for generating data concerning the dimensional size of thedefect being monitored and determining, according to preset tolerances,when the size of the defect exceeds acceptable limits. In order to carryout this size scaling function for both cracks or splits in veneer whichhave relatively large with-grain size with quite narrow cross-graindimension, and

monitor as well flaws refilled by knotholes and the like which havesubstantially larger cross-grain size, it is necessary for the logicportion of the computer to not only count the number and positionallocation of voids (corresponding to 1'5) occurring at scanner detectionpoints within a single pass line (i.e., strobe interrogation sequence)over the scanner head but also to compare the results of successivescanner pass lines. Accordingly, in order for the computer to properlyanalyze the data supplied by the output of the threshold detectorcircuit, it is necessary to provide means for accumulating the outputsof a plurality of successive pulse trains so as to generate informationrepresenting the size of any defect noted, both its cross-graindimension (i.e., parallel to the direction of strip travel) as wellasits with-grain dimension (transverse to strip travel). This type ofaccumulation can be readily effected by suitable shift registercircuitry known to the art, such as for example the shift registercircuit shown on page 5 of the publication by Texas Instruments entitledTTL Integrated Circuits. Counters and Shifts Register, Bulletin CA-102.

The accumulator in the logic portion of the computer accumulates theresults of successive outputs of the threshold detector circuit of FIG.6b so as to produce in successive intervals of time t,. .t compositewaveforms shown in the diagram of FIG. 60. Thus, considering for examplethe accumulator contents at time instant t it will be noted that thepulses or bits produced in the immediate time interval (t;) as well asthe two preceding intervals (t, and t are accumulated to produce acomposite pulse train having pulses at scanner detection points a, b,and c. Proceeding onward to the fifth time interval diagram (t thecontents of the accumulator which has now added the results of theimmediate as well as those of the preceding four time intervals,indicates a pulse or hit in all five of the positions a. .ecorresponding to scanner detection points, even though at time intervalt only a single pulse is produced, at location e, due to the presence ofa void at that particular scanner detection point. In this fashion theaccumulation of the results of a multiplicity of successive pulse trainwaveforms, each indicating the presence and relative lateral position ofvoids appearing in the strip material as detected by closelyspacedmonitoring points situated along the length of the strip as it travelsover the scanner, produces digital information for processing in thelogic portion of the computer which represents the with-grain dimensionof that the logic units can be divided into two parts, one, designatedas 60, for monitoring the size of cracks or splits in the wood which, asindicated earlier, have relatively large with-grain dimension, and theother, designated as 70, for monitoring the size of laws such asknotholes and the like which have relatively large cross-grain size.With regard to the former type of wood defect, the crack detection logic60 operates on the data provided by the output of the threshold detectorcircuit 54 to determine the with-grain dimension of each crack or splitappearing in the strip and compares the reading with a preset limit. Tothis end, the output of the threshold detector 54 is supplied to theaccumulator 62 previously described as being essentially a shiftregister for accumulating the contents of a plurality of successivescans (pulse trains) made by the inspection apparatus. A reset element64,,connected to receive inputs from both the threshold detector and theaccumulator, is used to clear the latter depending on theresult of themost recent scans and the contents of the accumulator at that time.Thus, for example, the reset could operate to clear the accumulatorcontents after the receipt of a predetermined number of scans unless thesubsequent scans contain input information which increase the contentsof the accumulator .(i.e., the number of stored pulses) therebyindicating that the crack defect under observation is either skewed withrespect to the grain or growing in size as the strip traverses past thescanner head.

The output of the accumulator, which itself is a pulse train indicating,as depicted in FIG. 6c, the number and position of voids (C s) noted atscanner detection points over an accumulation of successive scans, issupplied to a counter 66 which sums the total of such voids (EC togenerate an output representing the lateral or with-grain size of thecrack or split producing such voids in the strip. When the crackexceedsa certain with-grain size, as determined by comparison incomparator 68 of the output (2C of the counter 66 and a preset cracklimit (C,), the comparator element generates an output signal over line69 which can be used as an actuating signal to initiate the operation ofa clipper knife.

The second portion of the computer system, the flaw detection logic 70,simultaneously monitors both the with-grain and cross-grain size of anydefect noted in order to detect the presence of any open knothole or thelike whose area exceeds a certain size. A description of the design andoperation of this portion of the computer system is provided in theaforementioned US. Pat. No. 3,560,096 whose disclosure is hereinincorporated by reference.

In similar fashion to the crack detector logic 60, the flaw detectionlogic accumulates or stores the results of successive scans while alsoexamining the results of each scan line individually. Again, as an inputto the logic, the threshold detector 54 supplies the digitized pulsetrain representing the number and position of voids detected by thescanner at the instant of the strobe interrogation of the photosensorelements associated with each scanner detection point. A counter 72counts the number of pulses or bits detected at contiguous scannerdetection points and supplies this total (ZWG to a comparator 74 whichin turn compares the total of with-grain voids detected with a presetwith-grain limit (WG to generate an output on line 75 whenever thenumber of voids detected on a single scan line exceed the preset limit.(Typically the with-grain WG would be smaller than the crack limit C setin the crack detection logic so as to have the flaw detection logicrespond to the presence of defects in the veneer strip whose lateral orwith-grain dimension is not large enough to be classified as anunacceptable crack.)

The output of the with-grain comparator 74 is supplied to a secondcounter 76 which is designated as a cross-grain counter since itfunctions to ascertain the cross-grain size of any defect noted, i.e.,its size in the direction longitudinal of the strip. The countersummation (EXG derived from tallying the number of successive scanlinescontaining with-grain defects of excessive size, is supplied to a secondcomparator 78 which compares thisreading to a preset cross-grain limit(WG,,) so as to generate an output signal when a flaw of excessive sizeis detected.

The terms and expressions which have been employed in the foregoingabstract and specification are used thereinas terms of description andnot of limitation, and there is no intention, in the use of such termsand expressions, of excluding equivalents of the features shown anddescribed, or portions thereof, it being recognized that the scope ofthe invention is defined and limited only by the claims which follow.

What is claimed is:

1. In a scanner, for use in inspecting a moving strip of planar materialand responsive to incident light energy transmitted through openings orother defects appearing in said material, comprising an array offlexible, longitudinally-extending light-conducting optical fibers whosefirst terminal ends are respectively situated at spaced positionsproximate to said strip and extending transversely of the direction ofstrip movement, and whose second terminal ends are optically coupled inone-to-one relationship to a corresponding array of photoelectrictransducer elements for converting said incident light energy into anelectrical output, the improvement wherein the respective secondterminal ends of the array of optical fibers are each secured insidecorresponding bore openings formed in a block member which is adapted tomate with a keyway channel provided in a holder member, said holdermember containing the array of corresponding photoelectric transducerelements, the assembly of said block and holder members serving to holdand maintain said first terminal ends of said optical fiber array inpositional alignment with their respective photoelectric transducerelements.

2. A scanner according to claim 1 further comprising adjustable shuttermeans formed of longitudinallymovable thin, short strips of opaquematerial situated on one of said members between said respective secondterminal ends of said optical fibers and their associated photoelectrictransducer elements contained on said holder member, whereby theadjustment of the position of a respective strip blocks off a selectableportion of the light energy transmitted by the optical fiber associatedtherewith in order thereby to provide means for normalizing theresponses of said photoelectric transducer elements to a uniform level.

3. Flaw detection apparatus for inspecting a moving strip of planarmaterial comprising:

a. an illumination source on one side of said strip projecting lightthereon,

b. a scanner situated on the other side of said strip and producing anelectrical output in response to light transmitted through any openingsappearing in the material passing between said illumination source andsaid scanner,

. pulse converter means for converting said electrical output of saidscanner into a series of pulse train waveforms respectivelyrepresentative of the instantaneous light transmission pattern acrossthe width of the material taken at spaced locations along the length ofsaid strip,

. accumulator means for accumulating the results of a predeterminednumber of successive pulse trains corresponding to successive scans ofsaid material as it passes between said illumination source and saidscanner,

collected in said accumulator means,

. means for comparing the pulse total in said first counter with a firstpredetermined value so as to provide an output signal from saidapparatus when said value is exceeded, said output signal denoting thepresence of an opening in said strip whose major dimension exceeds atolerance limit,

. second counter means for totaling the number of pulses in each of saidpulse trains produced by said first counter means for totaling theresultant pulses Y from said apparatus denoting the presence of anopening in said material whose size exceeds a set of predeterminedtolerance limits on both its transverse and longitudinal dimensions.

a: a r a c Patent NO- 3,694,658 Dated Se tember 26, 1972 Inventor(s)Gerald L. Watson and Don Latshaw It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

" to or-.

Col. 4, Line 45 Change "on Col. 6, Line 16 Change "photodector" to-photodetector-.

Col. 6', Line 32 Change "crosssection" to crosssection-.

Col. 6, Line 61 Change "crosssection" to -crosssection-.

Col. 8, Line 59 Change "laws" to flaws.

Signed and sealed this 13th day of February 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PC4050 (10-69) USCOMM-DC wan-pea U.54 GOVERNMENTPRINTING OFFICE 2 9'9 0-353-3!

1. In a scanner, for use in inspecting a moving strip of planar materialand responsive to incident light energy transmitted through openings orother defects appearing in said material, comprising an array offlexible, longitudinally-extending lightconducting optical fibers whosefirst terminal ends are respectively situated at spaced positionsproximate to said strip and extending transversely of the direction ofstrip movement, and whose second terminal ends are optically coupled inone-toone relationship to a corresponding array of photoelectrictransducer elements for converting said incident light energy into anelectrical output, the improvement wherein the respective secondterminal ends of the array of optical fibers are each secured insidecorresponding bore openings formed in a block member which is adapted tomate with a keyway channel provided in a holder member, said holdermember containing the array of corresponding photoelectric transducerelements, the assembly of said block and holder members serving to holdand maintain said first terminal ends of said optical fiber array inpositional alignment with their respective photoelectric transducerelements.
 2. A scanner according to claim 1 further comprisingadjustable shutter means formed of longitudinally-movable thin, shortstrips of opaque material situated on one of said members between saidrespective second terminal ends of said optical fibers and theirassociated photoelectric transducer elements contained on said holdermember, whereby the adjustment of the position of a respective stripblocks off a selectable portion of the light energy transmitted by theoptical fiber associated therewith in order thereby to provide means fornormalizing the responses of said photoelectric transducer elements to auniform level.
 3. Flaw detection apparatus for inspecting a moving stripof planar material comprising: a. an illumination source on one side ofsaid strip projecting light thereon, b. a scanner situated on the otherside of said strip and producing an electrical output in response tolight transmitted through any openings appearing in the material passingbetween said illumination source and said scanner, c. pulse convertermeans for converting said electrical output of said scanner into aseries of pulse train waveforms respectively representative of theinstantaneous light transmission pattern across the width of thematerial taken at spaced locations along the length of said strip, d.accumulator means for accumulating the results of a predetermined numberof successive pulse trains corresponding to successive scans of saidmaterial as it passes between said illumination source and said scanner,e. first counter means for totaling the resultant pulses collected insaid accumulator means, f. means for comparing the pulse total in saidfirst counter with a first predetermined value so as to provide anoutput signal from said apparatus when said value is exceeded, saidoutput signal denoting the presence of an opening in said strip whosemajor dimension exceeds a tolerance limit, g. second counter means fortotaling the number of pulses in each of said pulse trains produced bysaid pulse converter means, h. means for comparing the total obtained bysaid second counter means with a second predetermined value so as toderive a second signal when said second value is exceeded, and i. thirdcounter means for counting the number of times said second signal isproduced and generating a third signal when the count in said thirdcounter exceeds a third predetermined value, said third signal servingas an additional output signal from said apparatus denoting the presenceof an opening in said material whose size exceeds a set of predeterminedtolerance limits on both its transverse and longitudinal dimensions.